Induction motor



Oct. 9, 1934. c. R. BooTHBY ET AL 1,975,598

INDUCTION MOTOR Filed sept. 1o, 1932 iiiwiw" WITNEssEs:

Vinton Eoozby l Patented "a. 9, 1934 vUNITED; STATES PATENT OFFICE INDUCTION MOTOR Application September' 10, 1932, Serial No., 632,502

` 3 Claims.

, Our invention relates to a starting device for induction motors, more particularly of the single phase type. and it has particular relation to automatic means for varying the reactance of the 5 rotor.

In starting induction motors, a low current in the rotor is desirable. This is especially' true of Asingle-phase induction motors. Considerable difficulty has been experienced in trying to control the starting current in the squirrel-cage type of rotor.

Itis, accordingly, an object of our invention to provide a novel means for varying the reactance in the rotor of an induction motor of the squirrelcage type during the starting operation and which l vmay also automatically operate a switch for openv ing the starting winding of the motor Another object of our, invention is to provide an eiiicient and economical means for bringing an 99 induction motor up to speed and interrupting the circuit oi the starting winding.

Another object of our invention is to provide a centriiugally operated device which effects a high refinance in the rotor upon starting and 9d which decreases the reaotance upon increase in the speed oi the rotor.

Another object oi our invention is to provide 'a higher minimum .u1-,1: torque for a given starting current in en induction motor.

@ther objects ci our invention will become evi dent from the following detailed description teiten in commotion' with the accompanying drawing, 'in winch-n Figure 'l is a longltil sectional view ci til induction tor provided with a eentriiugally opereied device in ordance with oar laverie tien;

2 is eievaticnoi view et a disc member,

his, 9 ci cennecticns oi stator oi motor.

T e in' We. i comprised a rotor il of an induction rooien oi the squirrel cage The rotoieosapeieec laiations i2 ed mounted on e shait'i9, the rotor having condoctor bara lli disposed near 'the periphery thereof parallel to the axis of the rotor, and the usual end rings 15.

Our automatic reactance and circuit-control-s ling switch 16 is mounted on shaft 13 and coin-a prises a disc 17 having a flanged hub 19 xedly mounted on the shaft, and a movable disc 19 of magnetic material disposed around the iianged hub 18. The movable disc 19 extends substantially parallel to the disc 17 and is mounted thereon by a plurality of bolts 21 rigidly secured to the disc 17 near its periphery. The movable disc 19 rotates with the disc 17 but is adapted to move laterally therefrom. By the provision of helical springs 22 surrounding the Shanks of bolts 21, the movable disc 19 is normally forced into engagement with the disc 17.

Movable disc 19 has; its outer peripheral portion 23 offset toward the conductor bars 14 so that the air gap between the portion 23 and the` end ring 15 will be as small as possible. The inner portion 24 of movable disc 19 is offset opposite to the outer portion 23 in order that centrifugally actuable weights or balls 26 may be disposed between the discs 17 and 19. The movable disc 19 has radial depressions 27, of decrease ing width toward the outer portion thereof, for guiding the balls 26 in their outward movement. The inner end of the offset portion 2e near the hub 19 is olset enough to'allow the balls 26 to rest between the members 17 and 19 when they are in engagement in their normal inoperative position. The spaces 27 between the members 17 and 19 decrease in Width toward the outer peripheries so that when the balls 26 move out Wardly because oi centrifugal force, the movable member 19 will be forced laterally away from the member 17 against the force of the springs 22.

Suitable axially extending rods 28 are secured to the movable member 19 and move longitudinally therewith. The rods 28 entend through suitable apertures 29 in the rotor and have a contact plate 3l secured to the opposite end there oi. Stationary brush members 32 mounted on a suitable insulating plate 33, may be associated with a starting winding 34a, constituting a part of the stator winding 34 and shown schematically in Eig.. 9, ior opening the starting winding when the rotor reaches a predetermined speed. The malin winding is indicated at 3th. The plate 33 may be supported by means of bolts 36 from one ci the bearing brackets o the motor, sleeves 37 entice bolts serving to space the plate from the bearing brochet.

ln operation, the movable disc 19, being oi lo@ magnetic material and close to one oi the end rings i5, causes a high reactance in the secondary circuit which lowers the starting current. At some predetermined speed as the motor acceler- 105 aies, which speed may be the operating speed of the starting switch, the balls 26 move radially outwardly in the radial grooves 27 and in turn move the disc 19 longitudinally against the force of the springs 22 away from thesrotor and the end ring 110 till) 15. As the disc 19 moves away from the end ring, the reactance in the rotor decreases.

This device gives a higher maximum running torque for a given starting current because the additional reactanceiwhich reduces the starting current is not effective when the motor is running. The balls will resume their normal inoperative position and the disc 19 will move to its original inoperative position upon the stopping of the motor, because of the force of the springs 22.

The contact plate 31 moves with the movable disc 19 and thereby moves away from the brush members 32 and breaks the starting winding circuit at a predetermined speed.

The device embodying our invention thus provides an eicient means for decreasing the current in an induction motor upon starting and for interrupting the circuit of the starting winding at a predetermined speed.

While wev have disclosed a preferred form of our invention for the purpose of illustration, it is to be understood that various modifications are contemplated Within the scope of the claims which follow.

We claim as our invention:

1. An alternating current motor including a starting winding and a squirrel cage rotor, an axially movable magnetizable plate at one end of the rotor, spring means for yieldingly pressing the magnetizable plate toward the rotor, circuit controlling means for the starting winding, and a centrifugally actuable device operatively associated with the rotor for simultaneously moving the plate away from the rotor and actuating the circuit controlling means to interrupt the circuit of the starting winding.

2. In an induction motor, in combination, a`

secondary winding, a starting winding, a centrifugally-operated device for controlling the reactance in said secondary winding and for opencircuiting said starting winding at a predetermined speed, said device comprising two discs, one of said discs being adapted to control the reactance of said secondary winding upon starting and being also adapted to cause open-circuiting of said starting winding at a predetermined speed, and a plurality of balls disposed between said discs for moving one of said discs laterally when said motor is operated.

3. An alternating-current motor including a squirrel-cage rotor having end rings thereon, a rotor shaft, a disc fixed on the shaft adjacent one end of the rotor, a magnetizable disc at said one end of the rotor movable axially of the shaft, resilient means operatively engaging both discs for pressing the magnetizable disc toward the xed.

. disc and close to one end ring, and centrifugallyactuable radially movable balls between the discs to move the magnetizable disc away from the end ring at a predetermined rotor speed.

CLINTON R. BOOTHBY. HARRY D. ELSE.

las n 

